1. Field of the Invention
The present invention relates to an exhaust gas purifying catalyst and a method for manufacturing the same, and more particularly to an exhaust gas purifying catalyst and a method for manufacturing the same which can reduce the manufacturing cost by reducing the used amount of a precious metal coated in the catalyst used to purify the exhaust gas of a vehicle while efficiently purifying the exhaust gas.
2. Description of Related Art
Recently, as the number of vehicles and the volume of traffic increases, the problem of air pollution due to exhaust gas has become a severe social problem.
Therefore, the governments of nations have determined discharge standards about exhaust gas contamination materials such as carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx), and the restrictions to the exhaust gas are gradually becoming more strictly.
Conventionally, in order to remove harmful materials from the exhaust gas of a vehicle, catalysts coated with precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) have been used. The catalysts are mounted to exhaust systems to remove harmful substances from the exhaust gas and purify the exhaust gas by expediting decomposition of hydrocarbon, oxidation of carbon monoxide, and deoxidation of nitrogen oxide.
A uniform coating catalyst obtained by uniformly coating a carrier with a precious metal is well known as an exhaust gas purifying catalyst.
On the other hand, recently, strict regulations on the exhaust gas discharged at the beginning of an engine start have been required. The exhaust gas is known to be discharged by sixty percent at the beginning of the engine start. However, in the case of the well known uniform coating catalyst since the engine is not warmed up sufficiently, the temperature of the exhaust gas is low and a relatively long time is required to reach the light off temperature, thereby lowering the efficiency of the exhaust gas purification at the beginning of the engine start. Therefore, catalysts which can be promptly warmed up and activated at the beginning of the engine start are required.
On the other hand, the well known uniform coating catalyst uses a large amount of the precious metal, increasing the manufacturing cost.
FIG. 1 is a view for showing the connection of exhaust manifolds and a catalyst converter of a vehicle. The exhaust manifolds function as passages of the exhaust gas discharged from the cylinders of the engine, and the exhaust gas passes a catalyst converter to which four cylinders are gathered to install a catalyst. However, as shown in FIG. 2, the flow amount of the exhaust gas passing through the catalyst converter varies according to the shapes of the exhaust manifolds. FIG. 2 shows the flow amount of the exhaust gas passed through portions a to d of FIG. 1.
However, since the uniform coating catalyst is coated with precious metal uniformly without considering the flow amount of the exhaust gas, precious metal is wasted on a portion at which the flow amount of the exhaust gas is relatively small. Since the precious metal is a material which has a small yield amount and is expensive, the precious resource can be saved by limiting the used amount of the precious metal, as there is the manufacturing cost of the exhaust gas purifying catalyst to be lowered.